U.S. Pat. No. 4,746,682 to J. Green relates to a polyurethane flame retardant containing a polybrominated diphenyl oxide and an alkylated triaryl phosphate ester.
Certain disclosures exist in the prior art in regard to organic diphosphates of the general class ##STR1## where R can be substituted or unsubstituted alkylene, arylene, alkylene arylene, or other divalent connecting radical (e.g., diphenylene sulfone -SO-, -S-, -SO.sub.2 -), and the like and R.sub.1 can be substituted or un-substituted aryl or alkyl. Examples of some disclosures include the following: U.S. Pat. Nos. 3,492,373; 3,869,526 and 4,203,888; British Patent No. 2,061,949; and Japanese Patent Publication Nos. 57/174,331; 71/22,584; 74/40,342 and 82/55,947.
Also relating to this class of compounds are copending U.S. patent application Ser. No. 374,717, filed Jul. 3, 1989, entitled "Novel Aromatic Bisphosphated" which covers compounds where R.sub.1 is aryl and R is --C.sub.6 H.sub.4 SO.sub.2 H.sub.4 -- and U.S. patent application Ser. No. 374,716, filed Jul. 3, 1989, also entitled "Novel Aromatic Bisphosphates" which covers compounds where R.sub.1 is also aryl and R is a neopentyl group of a halogenated neopentyl group.
U.S. Pat. No. 4,049,617 discloses a group of flame retardant phosphorus esters containing one to three 1,3,2-dioxophosphorinane rings. These flame retardants contain an hydroxyl radical so that they are capable of reacting into the polymeric chain of, e.g., polyurethane, thereby imparting a durable flame retarded polymeric composition.
Most of these flame retardants suffer from the drawback that when incorporated in polurethane compositions, they are too volatile or contain volatile impurities which will be released when the polyurethane is heated. This is becoming an increasingly significant problem in the automobile industry because the new aerodynamic designs employ, for example, a flatter windscreen which increases the surface area of sun penetration into the auto on warm, sunny days, This often leads to internal temperatures above 100.degree. C. and thus evolution of volatile products from polyurethane parts in the auto. These volatile products produce a thin film in the auto which is particularly noticeable on the windscreen. This phenomena has been termed, "fogging".
Automakers are beginning to demand polyurethanes which exhibit significantly less fogging in order to eliminate this problem. Accordingly, there is a need for flame retardant compositions which provide adequate flame retardancy in polyurethane foam compositions and reduce the amount of fogging which occurs upon heating of these compostions. This and other objects of the present invention will become apparent from the summary and detailed description which follow.